Preparation of Salts

An Interactive Guide to Mastering Salts

1. What is a Salt?

What is a Salt?

Click to reveal the definition.

A salt is a compound formed when the hydrogen atom in an acid is replaced by a metal. For example, replacing H in HCl with Potassium (K) forms Potassium Chloride (KCl).

Why are Salts Important?

Click to see their uses.

Salts have many important uses, including:

  • Fertilisers
  • Batteries
  • Cleaning products
  • Healthcare products
  • Fungicides

How do you Name a Salt?

Click to learn the rule.

A salt's name has two parts: The first part from the metal/base, the second part from the acid.

Hydrochloric Acid (HCl) → Chloride (Cl⁻)
Sulfuric Acid (H₂SO₄) → Sulfate (SO₄²⁻)
Nitric Acid (HNO₃) → Nitrate (NO₃⁻)

Test Yourself: Intro to Salts

1. Which acid produces sulfate salts?

2. What is formed when the hydrogen in an acid is replaced by a metal?

3. Reacting Zinc with Nitric Acid (HNO₃) produces which salt?

4. The salt Copper(II) Chloride is formed from which acid?

5. What is the first part of a salt's name derived from?

6. Which of these is NOT a typical use for salts?

7. What is the chemical formula for the nitrate ion?

8. If you react Magnesium with Sulfuric Acid, what is the name of the salt produced?

9. The chemical formula for sulfuric acid is H₂SO₄. The salt formed contains which ion?

10. A salt is what type of chemical compound?

2. The All-Important Solubility Rules

Soluble SaltsExceptions (Insoluble)
All NitratesNone
Most ChloridesSilver & Lead(II) Chloride
Most SulfatesBarium, Calcium & Lead(II) Sulfate
Insoluble SaltsExceptions (Soluble)
Most CarbonatesSodium, Potassium & Ammonium
Most HydroxidesSodium, Potassium & Ammonium
Remember SPA! Salts of Sodium, Potassium, and Ammonium are always soluble.

Test Yourself: Solubility

1. Is Lead(II) Sulfate soluble or insoluble?

2. Which of the following chlorides is insoluble?

3. According to the rules, which of these salts is always soluble?

4. Is Calcium Carbonate soluble or insoluble?

5. Which of these sulfates is INSOLUBLE?

6. The 'SPA' rule reminds us that salts of Sodium, Potassium and... which other cation... are always soluble?

7. You mix solutions and a precipitate of Barium Sulfate is formed. Is it soluble or insoluble?

8. Which group of salts has no exceptions to its solubility rule?

9. Is Copper(II) Hydroxide soluble or insoluble?

10. Which one of these carbonates is SOLUBLE?

3. Preparing Soluble Salts

Method A: Acid + Insoluble Substance

Use for reacting acid with an insoluble metal, metal oxide, metal hydroxide, or metal carbonate.

Acid + Metal → Salt + Hydrogen

Acid + Metal Oxide / Hydroxide → Salt + Water

Acid + Metal Carbonate → Salt + Water + CO₂

Note on Metals: Not all metals are suitable. Some (like Potassium) are too reactive, while others (like Copper) are not reactive enough.

Click to see the steps for Method A↓
  1. Gently warm the dilute acid.
  2. Add the insoluble substance a little at a time, stirring, until it is in excess (no more dissolves).
  3. Filter the mixture to remove the excess solid.
  4. Gently heat the solution to evaporate some water (saturate it).
  5. Leave the saturated solution to cool and crystallise.
  6. Remove crystals by filtration, wash with distilled water, and dry.
  7. (Refer to your textbook for the experimental setup diagram.)
    8. Experimental setup for preparing soluble salts
    Experimental setup for preparing soluble salts (warm acid, excess solid, filtration, evaporation, crystallisation). Tap to expand.
    Experimental setup for preparing soluble salts (expanded)

Method B: Titration

Use for reacting acid with a soluble base (alkali) or soluble carbonate. Needed because you can't see an excess of a soluble substance!

Acid + Alkali → Salt + Water

Click to see the steps for Titration↓
  1. Use a pipette for a precise volume of alkali in a flask.
  2. Add a few drops of indicator (e.g., methyl orange).
  3. Add acid from a burette slowly until the indicator just changes colour (the end point).
  4. Record the volume of acid added (the 'titre').
  5. Repeat with the same volumes but without the indicator to get a pure salt solution.
  6. Crystallise the salt from the pure solution as in Method A.
  7. (Refer to your textbook for the titration setup diagram.)
    8. Titration setup diagram
    Titration apparatus and end-point sequence. Tap to expand.
    Titration setup diagram (expanded)

Test Yourself: Preparing Soluble Salts

1. Which technique is used to prepare sodium chloride (a soluble salt) from sodium hydroxide (a soluble base)?

2. In Method A, why is the insoluble reactant added in excess?

3. What is the purpose of the indicator in a titration?

4. To prepare Copper(II) Sulfate from insoluble Copper(II) Oxide, which method is appropriate?

5. What piece of equipment is used to accurately measure a fixed volume of alkali into the flask for titration?

6. After filtering the excess solid in Method A, what is the next step?

7. Why is the titration repeated without the indicator?

8. Which of these reactions using Method A would produce hydrogen gas?

9. The process of forming crystals from a saturated solution is called:

10. Titration is necessary when reacting an acid with a...

4. Preparing Insoluble Salts (Precipitation)

This method, called precipitation, involves mixing two soluble salts to form one insoluble salt (the precipitate).

For example, to make insoluble Lead(II) Chloride, you mix soluble Lead(II) Nitrate and soluble Sodium Chloride.

Full Equation:

Pb(NO₃)₂(aq) + 2NaCl(aq) → PbCl₂(s) + 2NaNO₃(aq)

Ionic Equation:

The ionic equation shows only the ions that react. The other ions (Na⁺ and NO₃⁻) are spectator ions and are omitted.

Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s)

Click for the Precipitation Method steps↓
  1. Mix the two soluble salt solutions in a beaker.
  2. A solid precipitate will form instantly.
  3. Filter the mixture to separate the precipitate from the solution.
  4. Wash the precipitate with distilled water to remove impurities.
  5. Place the precipitate in a warm oven to dry.
  6. (Refer to your textbook for the filtration diagram.)
    7. Filtration diagram for precipitate
    Filtration and washing of an insoluble precipitate (precipitation method). Tap to expand.
    Filtration diagram for precipitate (expanded)

Test Yourself: Preparing Insoluble Salts

1. In the preparation of Barium Sulfate by precipitation, which of these pairs of solutions could be mixed?

2. What is the name given to the solid formed in a precipitation reaction?

3. What is the purpose of washing the precipitate with distilled water?

4. To form insoluble silver chloride, you could mix silver nitrate solution with...

5. In the reaction to form Lead(II) Chloride (PbCl₂), what are the spectator ions?

6. What technique is used to separate the insoluble salt from the solution?

7. Precipitation reactions require the mixing of two...

8. What does an ionic equation show?

9. After washing, how is the precipitate dried?

10. Which state symbol is used for a precipitate in a chemical equation?

5. Hydrated & Anhydrous Salts

Water of Crystallisation

This is water that is chemically bonded into the crystal structure of a salt. A salt containing this water is called hydrated.

The formula shows the number of moles of water per mole of salt. E.g., CuSO₄·5H₂O means 5 moles of water are bonded to 1 mole of copper(II) sulfate.

Comparing Hydrated and Anhydrous Salts

FeatureHydrated SaltAnhydrous Salt
Contains Water?YesNo
ExampleCuSO₄·5H₂OCuSO₄

Reversible Reactions & The Test for Water

Heating a hydrated salt removes the water, which is a reversible reaction:

Hydrated Salt ⇌ Anhydrous Salt + Water

This property is used to test for water:

  • Anhydrous Copper(II) Sulfate turns from White to Blue.
  • Anhydrous Cobalt(II) Chloride turns from Blue to Pink.

Test Yourself: Hydrated Salts

1. What colour change is observed when water is added to anhydrous cobalt(II) chloride?

2. What is the term for a salt that contains water of crystallisation?

3. What colour is anhydrous copper(II) sulfate?

4. The reaction: Hydrated Salt ⇌ Anhydrous Salt + Water is an example of what?

5. How can you convert hydrated copper(II) sulfate to anhydrous copper(II) sulfate?

6. In the formula CoCl₂·6H₂O, how many moles of water are there for every one mole of cobalt(II) chloride?

7. What is the chemical test for water?

8. What is the name for water that is chemically bonded into a crystal structure?

9. What colour is hydrated copper(II) sulfate?

10. What does the term 'anhydrous' mean?